Philip Larkin immortalised them in his poem At Grass. Old racehorses, their victories long forgotten, "stand anonymous again". The retired racehorses, Larkin claimed, "have slipped their names, and stand at ease, or gallop for what must be joy".

But for many horses the prospect of spending their final days in "unmolesting meadows" is little more than fantasy. New figures released by the government show that last year the total of all horses and ponies slaughtered for meat in England, Scotland and Wales rose to 7,933, representing a 50% increase on the average number slaughtered in previous years.

"A lot of that increase, at least half, will be thoroughbreds," said Dene Stansall, an adviser to Animal Aid, a charity that campaigns against the use of animals in sport. Stansall said a huge increase in the number of foals born to supply the racing industry, up from around 5,000 in 1960 to almost 19,000 a couple of years ago, was the main factor driving the slaughter of horses.

A spokesman for the British Horseracing Authority hit back at this claim. "The official figures, specifically in relation to Britain, simply do not back this up," he said. "It should be borne in mind that Animal Aid campaigns against horseracing and is on the record as saying it would like to see racing banned. This claim should be seen in that context."

Some racehorses will cease competing after three or four years, others will go on until into their teens, yet they can live for up to 30 years, so many will have decades ahead of them once they stop racing.

The foal oversupply is particularly acute in Ireland where there is an eight-week wait for horses to be slaughtered, resulting in a growing number being shipped to the UK to be shot and then bled.

The slaughter figures tell only part of the story. Many horses are sent to knackers' yards or turned into meat to feed hunt dogs, according to Animal Aid.

Finding the horses a home after they have raced is difficult, as cash-strapped families are also abandoning their animals, placing acute pressures on sanctuaries.

"The current recession has now added to an already critical situation and is starting to reflect heavily on the re- homing process of this sanctuary," said Graham Oldfield, of the Racehorse Sanctuary in West Sussex.

Roly Owers, chief executive of World Horse Welfare, said vets were reporting a rise in owners wanting their horses put down. "If an animal is older and perhaps not in the best health it may be better to have it kindly put to sleep than to sell or pass it on, when you don't know what kind of home it may go to, or whether it will end up in the meat market."

However, with each racehorse costing around £5,000 to look after per year, sending them to slaughterhouses is becoming an attractive option for owners who cannot sell them on. In 2009, Stansall estimated about 50% of racehorses in Ireland and 30% in England were failing to sell at auction. That proportion is expected to have risen last year.

Virtually all of the meat from horses slaughtered in the UK is exported to the rest of Europe, as it is still highly prized in some countries.

"Racehorses are always well stuffed with grub," Stansall said. "They are lean-looking animals, but don't get deceived by their thin legs. Look at the rump, there is lots of flesh."

He cited the fate of Capped For Victory, an eight-year-old once owned by Sheikh Maktoum Rashid al-Maktoum, the late ruler of Dubai, as that which typically befalls old racehorses. Imported from the US to Britain, where he raced 17 times, the horse was given away free at the end of his racing career. Within days of finishing 10th out of 12 runners in his final race, Capped For Victory had been killed, although how he died is unclear. "Whether or not he was rendered down or turned into meat I don't know," Stansall said. "But his meat carcass value would have been worth around £600."

Corran Ard, a prize-winning nine-year-old gelding, was retired from racing last year and was due to be slaughtered in France. He was saved at the last minute when an animal rights campaigner spotted him for sale on a website.

Animal charities accuse the racing industry, which races about 8,000 horses a year, of not doing enough to look after the animals once they have finished racing. However, the industry has been proactive in trying to secure homes for old racehorses. It pays for about 200 horses a year to be rehabilitated so that they can be ridden conventionally, although the process is expensive.

Financial pressures plaguing the racing industry are also being blamed. Many betting companies are locating offshore to avoid having to pay tax. As some of this tax has traditionally been distributed back across the racing industry, some trainers and owners are struggling to turn a profit.

"There's a major crisis," Stansall said. "You've probably got, say, 13 horses in a race at Wolverhampton or Southwell running for less than £2,000 prize money for first place. As a result there's been a big increase in horses abandoned." A BHA spokesman rejected this claim as without foundation.

Even valued horses can suffer this fate. Lady Margaret, who raced five times in a season and went into breeding as a brood mare, giving birth to three thoroughbred foals, died in 2010 aged 14 due to injuries caused by neglect.

Figures from the British Horseracing Authority show the recession is starting to have an impact on the breeding of thoroughbred horses, with the number of new foals being registered in Britain declining 23% between 2008 and 2010.

The BHA pointed to its own slaughter figures, based on official Food Standards Agency returns, of British-born horses registered with an independent company, Weatherbys. These showed 499 racehorses were slaughtered in 2010, a drop of 9% on the previous year. A total of 340 British-born and registered racehorses were slaughtered for meat in 2008. The BHA figures do not include thoroughbreds born abroad, chiefly in Ireland, that have never been in training in Britain or horses lost in the tracking system.

According to a BHA submission to parliament in 2009: "Thoroughbreds that have never raced are also killed in abattoirs; our initial analysis shows around 800 such animals in England, Scotland and Wales were in that category last year and a considerable proportion of these will be former breeding stock."

• This article was amended on 17 February 2011 to include quotes and figures from the British Horseracing Authority.